The president bears a heavy responsibility for the crisis on our border.

Could the flood of underage, would-be immigrants over the southern border be “Obama’s Katrina moment” as Susan Page of USA Todaywarned? No, it’s worse. Even the most virulent Bush denigrator would not suggest that the former president actually created the hurricane. This president, by contrast, bears a heavy responsibility for creating the deluge of unaccompanied minors who have recently crashed ashore.

To say that President Obama is largely responsible is not to say that he intended this result. If this episode serves to remind people about the law of unintended consequences, we’ll learn far more valuable lessons than those we drew from Katrina.

Some have argued that the William Wilberforce Trafficking Victims Protection Act, signed by President Bush on December 23, 2008, and designed to protect Central American children brought into the U.S. as sex slaves, is the true cause of the trouble in Texas now. While it is true that the law provides for different treatment of women and children from Central America than for Mexicans, it’s hard to sustain the case that the law created the surge in crossings.

As recently as 2011, three years after passage of the Wilberforce act, only 15,700 children were apprehended at the border. According to U.S. Customs and Border Protection, the number of unaccompanied minors from Central America began to rise in 2012 and has continued to increase sharply since then. Some 47,000 have been apprehended so far in 2014, and predictions are that up to 90,000 could enter this year.

The White House insists that the migrants are fleeing violence and poverty in their home countries. No doubt, but poverty and violence have (sadly) been features of those societies for decades.

What happened? The precipitating event was President Obama’s election-year decision unilaterally to grant permanent-resident status to the children of illegal aliens who had lived in the U.S. for a significant period of time and were brought here before the age of 16.

Clearly, the president was thinking about how this would play with voters, especially Hispanics. “They are Americans in their heart, in their minds, in every single way but one: on paper,” he said at the time, and this change (unlawful, but that’s another story), would make immigration policy “more fair, more efficient, and more just.”

There was another audience for the president’s words and deeds though. Rumors flew in Central America that children would no longer be deported from the U.S. There is now widespread talk of “permisos” — documents the migrants believe they will be granted if they get across the Rio Grande. As The Economistreports, a leaked border-agency memo described interviews with 230 women and children apprehended recently. Most reported that they came because they’d heard that they would be permitted to stay.

Defenders of the president’s decision say that it was “compassionate” to free people brought here by their parents from the fear of deportation. Maybe. It is difficult to live with the dread (if only notional) of deportation. But consider what sort of suffering the president’s policy has helped to create. What we’re seeing in Texas and elsewhere should remind us of the unintended consequences — namely that we have contributed to a humanitarian crisis.

Many of the migrants travel over dangerous territory on their journey north, vulnerable to everything from snakebites to thieves and rapists. The train through Mexico, dubbed “the Beast” by migrants, is so overcrowded that some travelers sleep on the metal fitting between boxcars. Many fall from the cars, losing limbs or their lives.

Once here, the migrants are housed in overcrowded facilities. In Arizona, the LA Timesreports, “most were corralled behind chain-link fences topped with razor wire, huddling for warmth on plastic mats under flimsy metallic Mylar blankets. . . . Banks of portable toilets served as sanitary facilities. Beside a recreation area, a camouflage tarp had been strung up to shield temporary showers.”

I am a believer in certain immigration reforms. But the moral of this story is that government should always be circumspect about its aims, modest in its efforts, and flexible in response to failure. Policies based on compassion may be worthy but flawed — as the Wilberforce law was. Or they may be reckless panders — as the president’s “DREAMers” executive order was.

The lesson everyone seemed to take from the Katrina mess was “Get rid of Bush.” The lesson of the southern border should be: “Consider the unintended consequences.”